1. Technical Field
The invention relates to an apparatus and method for maintaining a minimum state of charge on a motor vehicle battery.
2. Description of the Problem
Several classes of vehicles, particularly heavy-duty vehicles, spend substantial periods of times with their engines idling while supporting electrical loads. These loads can easily exceed the capacity of the vehicle's alternator to support the loads at diesel engine idle with the result that the loads become a direct drain on the vehicle's battery. Under these conditions battery voltage may drop low enough to kill the engine. Drivers have had to monitor battery voltage on the vehicle's instrument cluster and increase engine speed in response to declining battery voltage. Some vehicles have come equipped with preset or variable engine speed controls that can be enabled through vehicle cruise control switches or remote body mounted engine speed control switches for use if the vehicle is parked. Other vehicles, equipped for power takeoff (PTO) applications, provide for automatic increases in engine speed to supply increased engine power when the PTO is engaged. See for example U.S. Pat. No. 6,482,124 which is assigned to the assignee of the present application.